This invention relates to apparatus for processing web materials and, more particularly, to an apparatus for accurately controlling the processing time of web materials.
In the graphic arts field a mask containing an image opaque to actinic radiation often is used in preparing a printing plate both for letterpress and lithographic work. Such a mask is also used to prepare the initial contact or half tone films used for the subsequent preparation of printing plates. A similar mask is used in the preparation of printed circuit boards using photoresist materials. Film masks are known in the form of individual sheets or a continuous web, in which a base or substrate, typically plastic, is coated with a photosensitive (often resist-forming) material and is exposed to actinic radiation through a suitable half-tone mask. After exposure the film is treated with a processing portion depending upon the particular materials used.
Processing typically involves the so-called developing step in which the exposed photosensitive layer is either softened or hardened so that the soft or loose material may be removed. The next step is the washing or rinsing step whereby the softened regions are removed from the film typically by a high pressure spray. Following this the film is dryed.
In recent years some of the materials used in the photosensitive layers of the films and plates have been rapidly processable materials which reduce the processing time required. Furthermore, some of these materials are relatively soft and extremely sensitive to pressure marks which can be caused if the film is folded or bent during the processing.
With such rapidly processable materials, it is necessary to devise a processor which is capable of accurately and precisely controlling the development time such that various areas of the film are neither overdeveloped nor underdeveloped. Most prior art processors are not capable of such accurate control of processing time particularly when relatively short development times, typically a matter of a few seconds, are involved. Furthermore most processors of the prior art tend to have "turnarounds" which in bending the film back on itself tend to mark and otherwise damage, and hence lower the quality of, the films used.
Among the known prior art processors is one described in U.S. Pat. No. 2,404,138 issued July 16, 1946 to A .L. Mayer. The disadvantage of the Mayer processor is that the precise development time cannot be controlled accurately because the developer is not accurately and precisely applied to and removed from the film. There is no well defined starting and stopping point for the development process relative to the surface area of the film. Another system is that described in U.S. Pat. No. 3,448,720 issued June 10, 1969 to R. C. Graham. Here again the development time cannot be well defined or controlled, since there is no means of ensuring that the development chemicals cover a precisely defined surface of the film or plates. Still another system is that described in U.S. Pat. No. 3,710,703 issued Jan. 16, 1973 to Bruno et al. This system in addition to suffering from the inability to precisely control the development time, subjects the film to a tortuous path which tends to mark the film. Another U.S. Pat. No. 3,589,261 issued June 29, 1971 to Costas Krikelis, describes a system which although quite satisfactory for the purposes for which it was designed, has many of these same deficiencies.
Accordingly, it is an object of this invention to obviate many of the disadvantages of the prior art photosensitive material processors.
Another object of this invention is to provide an improved apparatus for precisely controlling the development time of a photosensitive material.